1. Field of the Invention
The present invention relates to a fluid reservoir tank for use with brake systems and clutch systems for automotive vehicles and, more particularly, to a fluid drop detecting reservoir tank which can detect a predetermined drop in the level of a fluid in the reservoir tank.
2. Description of Related Art
In order to install reservoir tanks of this kind in restricted spaces and assure certain fluid drop detection, it is typical to use fluid drop detecting means including, in combination, a magnetized float and a reed switch. Some fluid reservoir tanks with such fluid drop detecting means, which are used with, for instance, hydraulic brake systems for automotive vehicles, have magnetized floats disposed in fluid reservoir tanks and reed switch units removably mounted on or attached to the reservoir tanks.
A reservoir tank for use with a hydraulic brake system for an automobile vehicle is described in Japanese Utility Model Publication No. 62-35,635, for example. As shown in FIGS. 1 and 4, in this system, there is provided a float 4 with a magnet 3. The float 4 is movable up and down along a pair of vertical guide rails 2 in a cylindrical fluid container or reservoir tank 1. The reservoir tank 1 is provided, at its bottom, with a mounting casing 5 integrally formed with the reservoir tank 1. A reed switch unit casing 6 is removably inserted into and held in the reservoir tank 1. Within the reed switch unit casing 6, a magnetically operated, normally open reed switch 7 is disposed. The reservoir tank is assembled to a master cylinder 8 of a hydraulic brake system which is well known in the art.
As the volume of brake fluid in the hydraulic cylinder 8 decreases in quantity with the passage of time, hydraulic brake fluid contained in the reservoir tank 1 is supplementarily supplied to the master cylinder 8 so as to maintain a necessary quantity of brake fluid in the master cylinder 8. With a drop of the brake fluid in the reservoir tank 1, the float 4, floating in the brake fluid, slides downward along the guide rails 2. At a predetermined distance from the bottom of the reservoir tank 1, the float 4 places the magnet 3 in such a position that the magnet 3 effectively forces the reed switch 7 to turn on. Turning the reed switch 7 on causes a warning means to provide a warning that the fluid volume in the reservoir tank 1 is low.
Reed switch 7 is generally offset within the reed switch unit casing 6 either in a lengthwise direction or in a transverse direction of the reed switch unit casing 6 with respect to the center of the reed switch unit casing 6. To position the reed switch unit casing 6 at a predetermined position with respect to the magnet 3, the reed switch unit casing 6 should be positioned at a predetermined position in the mount casing 5 with respect to the reservoir tank 1. For this reason, the mount casing 5 is formed with a guide groove 9 extending in a direction in which the reed switch unit casing 6 is inserted. In addition, for preventing the reed switch unit casing 6 from coming out of the mount casing 5, the reed switch unit casing 6 is provided, at its forward end as viewed in a direction of insertion, with a stopper means, such as an elastically contractible projection 11. The elastically contractible projection 11 is contracted so as to pass through the guide groove 9 to an end opening 10 formed at the rear end of the mount casing 5. The reed switch unit casing 6 is forced into the mount casing 5, and the projection 11 elastically expands and is returned to its original shape in the end opening 10. The reed switch unit casing, therefore, firmly engages with and is retained by the rear end of the mount casing 5 when the reed switch unit casing 6 is properly positioned within the mount casing 5.
Because the elastically contractible projection requires a great thrust force in order to be contracted, the elastically contractible projection makes it difficult to demount the reed switch unit casing 6, which firmly engages with and is retained by the rear end of the mount casing 5, from the mount casing 5. In addition, because the elastically contractible projection is provided at the forward end, in a direction of insertion, of the reed switch unit casing 6, it is forced to strongly rub against the guide groove while the reed switch unit casing 6 is mounted and demounted. The projection, consequently, may be broken.